In the fabrication of semiconductor devices, a semi-conducting wafer must be processed in a large number of processing steps for producing integrated circuit chips on the wafer. These processing steps may amount to as many as several hundred or more. The various processing steps are conducted in a variety of processing machines to carry out a large number of chemical or physical reactions on the semi-conducting wafer. In the various fabrication steps, a large variety of chemicals including gases and liquids are utilized either as raw materials in a deposition process, as dopants in an implantation process, as an etchant in a wet or dry etching process, or as a chemical reactant in any other processes.
Since a large number of chemicals utilized in a semiconductor fabrication facility are of the flammable or toxic nature, i.e., other than those inert gases normally utilized as purge or carrier gases, the storage and transporting of such chemicals are important aspects in the management of a fabrication facility. For instance, to avoid fire, explosion and serious personal injuries, a flammable or toxic gas must be securely stored in a safe storage facility. The storage of these gases is usually kept away from the plant personnel and thus, away from the processing equipment where they will be used. The transporting or delivery of these gases to a processing equipment therefore becomes another important aspect in the management of a fabrication plant.
A typical gas delivery system utilized in a semiconductor fabrication facility is shown in FIG. 1. The system 10 includes a main process gas input line 12 and a main purge gas supply line 14. A process gas, after being fed into the main process gas input line 12, is transported through a two-way air actuated valve 16 into a main process gas supply line 18. Off the main process gas supply line 18, a number of two-way, diaphragm-type (hereinafter, diaphragm) control valves 20 are utilized to feed the process gas from the main supply line 18 into a three-way diaphragm control valve 24. Into the three-way diaphragm control valve 24, a purge gas is also fed from the main purge gas supply line 26 into a second gas inlet 28 of the three-way diaphragm control valve 24. The purge gas, i.e., an inert gas, fed through the inlet 28 is then mixed with the process gas fed through the inlet 22 and outputted from outlet 32 of the three-way diaphragm control valve 24. It should be noted that in the above example, the purge gas is utilized as a carrier gas for the process gas. The purge gas may also be used alone for purging the gas line without the process gas. In such application, the three-way diaphragm control valve is adjusted such that only inlet 28 is connected to outlet 32 of the valve, while inlet 22 is shut-off.
When the purge gas is used as a carrier gas, the gas mixture is sent through a gas pressure regulator 36, a pressure transducer 38 into a second three-way diaphragm control valve 42 through inlet 40. The process gas/carrier gas mixture then exits from either outlet 46 or 48 and is fed into a process equipment. It should be noted that in FIG. 1, the process equipment and the gas lines feeding to the process equipment are not shown for simplicity reasons. When the gas outlets 46, 48 are not connected to a process equipment or to a gas delivery line, the outlets 46, 48 are capped by a cap 50. In the gas distribution system 10 shown in FIG. 1, the main process gas input line 18 is further provided with an expansion valve 60. The expansion valve 60 is provided such that other gas output lines may be connected thereto allowing future expansion of processing equipment in the fab facility. The outlets 62, 64 are also capped by caps 66 when the expansion valve 60 is not in use for add-on additional gas supply lines.
In the gas distribution system 10, it is seen that a number of two-way or three-way diaphragm-type control valves, i.e., 20, 24 and 42 are utilized for controlling the flow of various gases, including those of the flammable or toxic nature or vacuum in the supply lines. The control valves are equipped with control handles mounted on top of the valves such that a handle may be turned either clockwise or counterclockwise to close or open the gas passage. The control valves can be accidentally turned and thus releasing the vacuum in the line.
As shown in FIG. 1, when the gas line between the two control valves 20, 42 has been evacuated into a vacuum state, and that the main process gas supply line 18 is connected to a pressurized flammable gas supply, any accidental opening of the control valve 20 may cause the flammable gas to enter the gas line between valves 20 and 42. A flammable gas that is frequently utilized in a semiconductor fab plant is silane which readily ignites when mixed with air, or with oxygen in the air. Consequently, when cap 50 is later removed for connecting to a process equipment, the moment silane gas contacts the atmospheric air, a fore ignites in the gas line between valves 20, 42. If valve 20 has been left open, the fire propagates through the main process gas supply line 18 and causes further damages to other process gas feed lines and other process equipment.
The accidental opening or closing of valves can therefore cause serious consequences in a semiconductor fab plant that utilizes flammable or toxic gases. In the above described situation, even when the operator, after accidentally opened the control valve 20, subsequently closes it, a serious hazard has already been created in the gas line since it is now filled with a flammable gas that is unknown to other plant personnel. When the gas line is accidentally filled with a toxic gas, serious personal injuries can occur to a machine operator when cap 50 is subsequently removed for connecting to other gas lines or to a process equipment.
It has been found that accidental tampering with a gas control valves in the gas distribution system has been a main cause for serious fires in many semiconductor fab plants. Even when fire does not occur, serious personal injuries has occurred to machine operators when a gas line is accidentally filled with a toxic gas. An effective means to prevent such mishaps is therefore desperately needed in a semiconductor fab plant that utilizes a gas distribution system.
It is therefore an object of the present invention to provide a gas distribution/control system for use in a semiconductor fabrication facility that does not have the drawbacks or shortcomings of a conventional gas distribution/control system.
It is another object of the present invention to provide a gas distribution/control system in a semiconductor fabrication facility that can be easily implemented without making substantial modification to the plant equipment.
It is a further object of the present invention to provide a gas distribution/control system in a semiconductor fabrication facility that can be effectively used without accidental opening/closing of control valves.
It is another further object of the present invention to provide a valve safety lockout device that can be made readily available in a semiconductor fabrication facility.
It is still another object of the present invention to provide a valve safety lockout device that can be utilized at low cost to effectively prevent accidental opening/closing of valves.
It is yet another object of the present invention to provide a valve control handle safety lockout device that can be used to lock a valve control handle so that any tampering of the lockout device can be easily identified.
It is still another further object of the present invention to provide a method to safety lockout a valve control handle by locking a single use lockout device onto a valve control handle while allowing visual inspection of the opening/closing status of the handle.
It is yet another further object of the present invention to provide a safety lockout device for a valve control handle that is fabricated in rigid plastic such that after mounting to a control handle, the device can stand up to compressive forces placed on the device without affecting the control handle.